The present invention relates to polymers comprising structural units which contain alkylalkoxy groups, and blends which comprise the polymers according to the invention. The invention is also directed to the use of the polymers and blends according to the invention in opto-electronic devices and to these devices themselves.
Electronic devices which comprise organic, organometallic and/or polymeric semiconductors are being used ever more frequently in commercial products or are just about to be introduced onto the market. Examples which may be mentioned here are charge-transport materials on an organic basis (for example hole transporters based on triarylamine) in photocopiers and organic or polymeric light-emitting diodes (OLEDs or PLEDs) in display devices or organic photoreceptors in copiers. Organic solar cells (O-SCs), organic field-effect transistors (O-FETs), organic thin-film transistors (O-TFTs), organic integrated circuits (O-ICs), organic optical amplifiers or organic laser diodes (O-lasers) are in an advanced stage of development and may achieve major importance in the future.
Many of these electronic devices have, irrespective of the respective application, the following general layer structure, which can be adapted for the respective application:    (1) substrate,    (2) electrode, frequently metallic or inorganic, but also comprising organic or polymeric conductive materials,    (3) charge-injection layer(s) or interlayer(s), for example for compensation of the unevenness of the electrode (“planarisation layer”), frequently comprising a conductive, doped polymer,    (4) organic semiconductor,    (5) optionally further charge-transport or charge-injection or charge-blocking layers,    (6) counterelectrode, materials as mentioned under (2),    (7) encapsulation.
The above arrangement represents the general structure of an organic electronic device, where various layers may be combined, meaning that in the simplest case an arrangement results from two electrodes, between which an organic layer is located. The organic layer in this case fulfils all functions, including the emission of light. A system of this type is described, for example, in WO 90/13148 A1 on the basis of poly(p-phenylenes).
In the case of a solution-processed system, this individual layer can either be a copolymer, in which case the corresponding functional units are present in the main chain or side chain of the polymer, or it can be a polymer blend, in which case different polymers comprise one or more functional units as structural units, or it may comprise soluble small molecules or mixtures of one or more polymers with one or more small molecules. All variants exhibit advantages and disadvantages. However, a main problem is the operating voltage of such systems, which is still relatively high, inadequate efficiency and an inadequate lifetime.
Solution-processable materials for OLEDs have caused a lot of excitement recently, in particular for a new generation of flat screens or as lighting element. Although great improvements in solution-processed OLEDs have been achieved in recent years, they still exhibit deficits with respect to their efficiency and lifetime compared with vacuum-evaporated SMOLED devices. By contrast, the advantage lies in simple processing from solution, where various layers can easily be produced by known coating methods (printing, spin coating), in contrast to a complex vapour-deposition process in a vacuum chamber.
Colour homogeneity is also in some cases very difficult to establish in the case of vapour-deposited small molecules, since small amounts of a dopant have to be dispensed accurately. In the case of copolymers, polymer blends or small molecules in solution, the requisite components, such as, for example, emitters or charge-transport units, can be dispensed very accurately in the correct concentration.
Many OLEDs in accordance with the prior art comprise an active polymer within a layer, where the polymer comprises all requisite functional units. This polymer layer is frequently applied to an interlayer, which is responsible, for example, for hole injection.
Polymer blends can also be employed and may be useful for various purposes, for example for white-emitting devices via a mixture of polymers emitting in different colours (turquoise and yellow, red, green and blue in increasing concentrations, for example GB 2340304), for improving hole injection in order to render an interlayer superfluous (for example WO 2008/011953), or in order to adapt the rheological properties by employing polymers having different properties.
Polymer blends frequently do not exhibit advantages overall over copolymers, but are nevertheless employed. However, systems in which the blend produces additional advantages over a copolymer would be advantageous. In WO 99/48160, an advantage of this type is achieved for the performance data of the OLED produced: a mixture is used in which the highest HOMO (highest occupied molecular orbital) in the mixture and the lowest LUMO (lowest unoccupied molecular orbital) in the mixture are localised on two different components, i.e. these two components form a so-called “type II heterojunction”, i.e. the component having the higher HOMO also has the higher LUMO. Thus, the separation between the HOMO relevant for hole injection and the LUMO relevant for electron injection is reduced without the band gap of the individual components being reduced and thus the emission colour being shifted to lower energy. Charge-carrier injection is thus simplified independently of the emission colour of the OLED component, i.e. also for deep blue-emitting OLEDs.